In IEEE 802.16 Uplink Partial Usage of SubChannels (“PUSC”) permutation, the minimal signal unit for receiver processing is a tile as shown in FIG. 2. A tile comprises four consecutive tones in the frequency domain and three consecutive Orthogonal Frequency Division Multiple Access (“OFDMA”) symbols. Six tiles chosen according to a pseudo random hopping sequence comprise a subchannel. A collection of subchannels used to transmit to a particular user is called an allocation. The OFDMA tiles hop around in a frequency-time grid to facilitate tone-hopping for interference mitigation where this hopping pattern is unique for each cell. The four pilot symbols (tones) existing in a tile are simply binary-phase key shifting (“BPSK”) symbols and therefore there are only a total of 16 possible different pilot sequences.
In the PUSC uplink of an 802.16 system, a base station receives a PUSC tile from a desired user (the desired user is also known as a target device). This tile may be interfered with by one or more PUSC tiles received from other sectors and/or another cells. One way to suppress the interfering tiles is to employ an array of receive antennas at the base station and use one of the interference suppression methods known in the art. These interference suppression methods can be broken into two categories: ones that require knowledge of the pilot symbols to both the desired user and all interference and methods that do not require knowledge of the interferers' pilot symbols but require an estimate of the spatial correlation matrix of the interference.
The first set of methods (the ones that require knowledge of the interferers' pilot symbols) clearly work well only if the interferers' pilot symbols are known. However, the knowledge of the interferers' pilot symbols is very difficult in cellular systems especially when the interferers are in other cells. The other category of interference suppression methods try to estimate the spatial correlation matrix to the interference by first estimating the channel to the desired user and then canceling an estimate of the desired user's signal on the pilots, thereby leaving only interference. One problem with these methods is that if the interference is very strong the channel estimation to the desired user is poor which results in some of the desired signal still being present when the spatial correlation matrix to the interference is estimated. The resulting interference suppression weights then suppress some of the desired signal along with the interference resulting in poor performance.
Therefore a need exists to overcome the problems with the prior art as discussed above.